Add support for fish subshell prompt (with patch)

[chown]

Current support for fish subshell doesn't show a prompt, because fish_prompt function is overridden to pass current path to mc.

Attached is a patch containing a change to allow a prompt function to be used.

The user can specify a fish_prompt_mc function to use a mc specific prompt, if none is specified fish_prompt is copied to fish_prompt_mc to use the default prompt. The new implementation of fish_prompt calls fish_prompt_mc to display a prompt before exit. Cwd is passed to mc as before.

The length of the command string is now over the limit of BUF_SMALL size, so I also increased it to BUF_MEDIUM.

GNU Midnight Commander 4.8.12-12-g4253f59
Built with GLib 2.40.0
Using the S-Lang library with terminfo database
With builtin Editor
With subshell support as default
With support for background operations
With mouse support on xterm
With support for X11 events
With internationalization support
With multiple codepages support
Virtual File Systems: cpiofs, tarfs, sfs, extfs, ftpfs, sftpfs, fish
Data types: char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;

[chown]

diff file

[chown]

Forgot to mention, tested on Ubuntu 14.04 with fish 2.0.0

[andrew_b]

Patch applied. Thanks!

Branch: 3232_fish_prompt
changeset:6d6bc23f2537a3b94910cee7b6d37bf7f70a0cec

[andrew_b]

Merged to master: [6d6bc23f2537a3b94910cee7b6d37bf7f70a0cec].